For large ships, in order to keep its balance during sailing, appropriate volume of seawater needs to be stored in the ballast tank at the bottom of the ship. The seawater or fresh water stored in the ballast tank for keeping balance of ship is known as ballast water.
Usually, ballast water is stored in the ballast tank near the port of departure, and after a voyage discharged from the ballast tank in the offshore area near the port of destination.
However, the ballast water charged into the ballast tank of the ship in the offshore area near the port of departure contains a variety of microbes that live in the offshore area or silt, and therefore the ballast water will pollute the offshore environment near the port of destination when it is discharged.
To solve the problem, a treaty for regulation and management of ship ballast water and sediments (hereinafter referred as “Treaty for Ballast Water”) is adopted, and it specifies the discharge standard of ballast water. Ballast water is prohibited to discharge if the discharge standard is not met.
To meet the ballast water discharge standard, a variety of proposals for installation of ballast water treatment system in ship are put forth. The Korean Patent Application No. 10-0743946, titled as “Apparatus for Purifying Ballast Water and Ship Mounted the Same”, describes a method, wherein the ballast water stored in the tank is treated with a filtering apparatus during storage, and the ballast water is sterilized with a sterilizing apparatus before it is discharged, which is to say, large-particle materials are filtered off with the filtering apparatus, and then a variety of planktonic organisms or microbes are sterilized under UV irradiation with the sterilizing equipment.
The present ballast water treatment systems mounted inside ships are not highly reliable, and their sterilization and purification effects are not ideal. Therefore, the ballast water still brings pollution to the offshore environment of the port of destination.